Archaea

Bacteriorhodopsin

A transmembranous protein to which retinal is bound; it functions as a light-driven proton pump, allowing photophosphorylation without chlorophyll or bacteriochlorophyll; found in the purple membrane of halophilic archaea

Methanogen

Pseudomurein

A peptidoglycan-like polymer found in some archaeal cell walls; it is distinguished from peptidoglycan by the presence of L-amino acids, N-acetyltalosaminuronic acid (NAT) and beta (1 to 3) glycosidic bonds

Sensory rhodopsin

Thermoacidophiles

Euryarchaeota

Occupy many different ecological niches and have a variety of metabolic patterns; includes methanogens, extreme halophiles, sulfate reducers, and many extreme thermophiles with sulfur-dependent metabolism